[Lug-nuts] Privacy

I know that there are a lot of ways to have your online activity tracked. And, I thought I understood many or most of them. But, I tried out Gemini with the request, "write a two page article on Stoicism." The results were interesting and pretty good and give me an idea of what Gemini can do. A week, or less later, yesterday, I get an email from Facebook suggesting that I join the "Daily Stoicism" group. WTF. I never use Facebook and basically ignore their reminders on how many notifications or messages I have. AFAIK, there is no legal way Facebook should know what I am doing with Google, unless Google is providing them the information on a back channel. Am I missing something? Everything I know suggest that I would have had to visit a Facebook site sometime between my Gemini request and my receipt of an email from Facebook. Or possibly have visited a Facebook site before my Gemini request and not have directly entered a URL or used a bookmark in the interim. AFAIK, those things didn't happen.